Choosing the right building materials

The best way for me to explain the concept of choosing materials is to run over my own thought process for choosing the materials I made my house out of. Your situation will be different and so your logic will differ, if only in being better suited to your situation.

I spent many years deciding what material to use for the walls of my home. At the same time I was working on the basic structure of the house and with each material I ended up figuring out how to build the design with that particular material. Had the design been a straight sided structure with right angles this would not have been the case, however, curved walls are a different animal and must be treated with some forethought.

My basic house design was round. This ruled out basic frame construction, which by it’s very nature is suited to straight walls. I also wanted a very energy efficient wall, so infiltration was not good but high thermal mass and/or insulation value was preferred. The best of both worlds would be an insulating material that also had considerable thermal mass. Insulated Concrete Forms seemed promising, but only in a form that didn’t lock the pieces together in straight lines and 90 degree angles. I needed to be able to stack these in a circle. I also wanted to make use of recycled materials if possible.

I considered the following options:

Rammed earth

This intrigued me for a long time as it seemed to embody the spirit and soul of thermal mass. Plus, it was plastic in the sense that it could be built to any shape and thickness. You can’t get much greener than sandy loam.

In the long run I decided against this because

I am no longer young enough to abuse my body beating on dirt for months at a time in the hot sun.

Even though I am in a dry climate, I worry about the effect of a driving rain on the walls

Uninsulated thermal mass means you eventually heat/cool the outdoors.

The soil in my area has a high radon content. Any building with thick earthen walls could be a death trap.

Poured earth

This is largely the same as rammed earth except for less pounding.

Straw bale

This is the opposite of rammed earth in that it embodies strong insulation but with little thermal mass. It also usually requires a separate frame for holding up the roof. My main reasons for rejecting this option were:

Lack of real straw bales (as opposed to hay) in my area.

Rodent problems during and after construction

The need to seal the bales as soon as possible after placement.

Mold issues. – My wife has strong allergies, especially to mold

Durisol blocks

These blocks, built of wood chips and fly ash looked promising. They are small enough to be easily moved, stack-able and flexible.

I could not find a local distributor for this product. As it was shipping from eastern Canada, it seemed like too much to deal with, plus it’s not a great green choice when it requires shipping a ton or more of bulky objects 2000 miles.

Corrugated Steel (think Grain Bins)

The only advantage a grain bin has over other options is that it’s already in a round shape and would assemble quickly, including the roof. I had an opportunity to get one at an auction in Wyoming and passed it up. It was the only way to get one cheaply. My reasons against it:

Not cheap, not even close

No insulation, no thermal mass, no green appeal.

Difficulty of insetting doors, windows…

When it rains or hails it’s so noisy you can’t hear yourself scream.

The only place where some wall segments would be worth having is for using as a form for a round foundation. Even so, you’d have to have two different sizes a foot or so different. This ends up being very expensive.

Rastra/PerformWall

The choice I finally went with. I had avoided it because I wasn’t too sure about having polystyrene in the wall, even though it would help with insulation. I finally saw some at an energy fair and liked the material after I saw it. There is a tendency to denigrate cement based products in Green circles due to the amount of energy it takes to produce it. Unfortunately, as long as building codes require concrete foundations and stem walls, there is no getting away from it. In this case it is a strong binder for holding the styrene chips together.

Pros

Available locally at the time

Good thermal mass/insulation combined

Workable by hand to form house shape and install nailers for openings and cabinets